The invention discloses a dendritic crystal growth numerical simulation method in a nickel-based alloy multi-pass surfacing process. The method comprises the following specific steps: defining the shape of a first surfacing welding pool, and establishing a dendrite nucleation and growth model and a solute distribution and diffusion model, secondly, defining the shape of a second surfacing weldingpool on the basis of the first surfacing welding, establishing a dendrite nucleation and growth model and a solute distribution and diffusion model, finally writing a computer program, inputting alloythermophysical parameters and various welding process parameters, importing simulation calculation software, and performing calculation to obtain a simulation result. Compared with experimental research, the method consumes less time and saves more maternal and labor resources, influences of microstructure morphology evolution, solute concentration distribution, welding current, welding voltage,thermal disturbance amplitude and other parameters on dendritic crystal growth in the nickel-based alloy multi-pass surfacing process can be simulated, and therefore a certain reference effect is achieved for selection and formulation of the nickel-based alloy multi-pass surfacing welding process.